Methods and apparatus to assist and facilitate vessel analysis

ABSTRACT

A method for analyzing a tubular structure in a patient includes receiving a cursor first position within a displayed tubular structure representative of the tubular structure in the patient, determining a path inside the tubular structure based only on the received cursor first position, and moving a cursor along the path by a pre-determined distance in a pre-determined direction to a cursor second position.

BACKGROUND OF THE INVENTION

This invention relates generally to methods and apparatus for analysisof vessel images, and more particularly to methods and apparatus forassisting medical care personnel such as radiologists in preparingmeasurements and reports during radiological examinations from imagesderived from computed tomographic, MR, and 3D radiation imaging.

In at least some computed tomography (CT) imaging system configurations,an x-ray source projects a fan-shaped beam which is collimated to liewithin an X-Y plane of a Cartesian coordinate system and generallyreferred to as the “imaging plane”. The x-ray beam passes through theobject being imaged, such as a patient. The beam, after being attenuatedby the object, impinges upon an array of radiation detectors. Theintensity of the attenuated beam radiation received at the detectorarray is dependent upon the attenuation of the x-ray beam by the object.Each detector element of the array produces a separate electrical signalthat is a measurement of the beam attenuation at the detector location.The attenuation measurements from all the detectors are acquiredseparately to produce a transmission profile.

In known third generation CT systems, the x-ray source and the detectorarray are rotated with a gantry within the imaging plane and around theobject to be imaged so that the angle at which the x-ray beam intersectsthe object constantly changes. X-ray sources typically include x-raytubes, which emit the x-ray beam at a focal spot. X-ray detectorstypically include a collimator for collimating x-ray beams received atthe detector, a scintillator adjacent the collimator, and photodetectorsadjacent the scintillator.

One application of computed tomographic (CT) imaging, as well asmagnetic resonance (MR) imaging and 3-D x-ray imaging (3DXR), isvascular analysis. X-ray quantification and analysis of vesselpathologies are important for radiologists who are called upon to assessstenosis or aneurysm parameters, quantify lengths, section sizes,angles, and related parameters. In some known imaging systems, analysisof vessel pathologies using three-dimensional data, such as CT, MR or3DXR.

Analysis of visual pathologies may sometimes be difficult since theoperator has to track possibly tortuous structures. These imagingsystems may include a method whereby a path is located between astarting point and an ending point, then the operator navigates alongthe calculated path with the aid of simple interface devices, such assliders or scrollbars which may increase the computer time required todefine and calculate the paths. Further, in the case of occlusions ordiscontinuous paths additional steps may be required to view thestructure.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method for analyzing a tubular structure in apatient is provided. The method includes receiving a cursor firstposition within a displayed tubular structure representative of thetubular structure in the patient, determining a path inside the tubularstructure based only on the received cursor first position, and moving acursor along the path by a pre-determined distance in a pre-determineddirection to a cursor second position.

In another embodiment, a method for reviewing a tubular structure over apassage of time is provided. The method includes providing at least afirst three-dimensional data set at a first time and a secondthree-dimensional data set at a second time representative of the sametubular structure, generating a first view of the firstthree-dimensional data set and a second view of the secondthree-dimensional data set, and positioning a first cursor at a firstthree-dimensional location within the first view and positioning asecond cursor at a first three-dimensional location within the secondview corresponding to the first cursor location in the first view. Themethod also includes determining a path inside the tubular structure,defining a direction from the cursor position in at least one of thefirst view and the second view, and moving the first cursor along thedetermined path by a pre-determined distance in a pre-determineddirection to first cursor second position and moving the second cursoralong the determined path by a pre-determined distance in apre-determined direction to second cursor second position.

In a further embodiment, a computer readable medium encoded with aprogram executable by a computer for analyzing a tubular structure in apatient is provided. The program is configured to instruct the computerto receive a cursor first position within a displayed tubular structurerepresentative of a tubular structure in a patient, determine a pathinside the tubular structure based on the received cursor firstposition, wherein the determined path includes a determined endpoint,and move a cursor along the path by a pre-determined distance in apre-determined direction to a cursor second position.

In yet another embodiment, a medical imaging system for analyzing atubular structure in a patient is provided. The medical imaging systemincludes a detector array, at least one radiation source, and a computercoupled to the detector array and radiation source. The computer isconfigured to receive a cursor first position within a displayed tubularstructure representative of the tubular structure in the patient,determine a path including an endpoint inside the tubular structurebased on the received cursor first position, and move a cursor along thepath by a pre-determined distance in a pre-determined direction to acursor second position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a CT imaging system.

FIG. 2 is a block schematic diagram of the system illustrated in FIG. 1.

FIG. 3 is a flowchart of an exemplary embodiment of a method foranalyzing a tubular structure in a patient.

FIG. 4 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 5 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 6 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 7 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 8 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 9 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 10 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 11 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure,

FIG. 12 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 13 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 14 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 15 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 16 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 17 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 18 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 19 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 20 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 21 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

FIG. 22 is a portion of the method illustrated in FIG. 3 for analyzing atubular structure.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the present invention, computed tomographic imagesare used. Referring to FIGS. 1 and 2, a computed tomography (CT) imagingsystem 10 is shown as including a gantry 12 representative of a “thirdgeneration” CT scanner. Gantry 12 has an x-ray source 14 that projects abeam of x-rays 16 toward a detector array 18 on the opposite side ofgantry 12. Detector array 18 is formed by detector elements 20 whichtogether sense the projected x-rays that pass through an object, such asa medical patient 22. Each detector element 20 produces an electricalsignal that represents the intensity of an impinging x-ray beam andhence the attenuation of the beam as it passes through object or patient22. During a scan to acquire x-ray projection data, gantry 12 and thecomponents mounted thereon rotate about a center of rotation 24. In oneembodiment, and as shown in FIG. 2, detector elements 20 are arranged inone row so that projection data corresponding to a single image slice isacquired during a scan. In another embodiment, detector elements 20 arearranged in a plurality of parallel rows, so that projection datacorresponding to a plurality of parallel slices can be acquiredsimultaneously during a scan.

Rotation of gantry 12 and the operation of x-ray source 14 are governedby a control mechanism 26 of CT system 10. Control mechanism 26 includesan x-ray controller 28 that provides power and timing signals to x-raysource 14 and a gantry motor controller 30 that controls the rotationalspeed and position of gantry 12. A data acquisition system (DAS) 32 incontrol mechanism 26 samples analog data from detector elements 20 andconverts the data to digital signals for subsequent processing. An imagereconstructor 34 receives sampled and digitized x-ray data from DAS 32and performs high-speed image reconstruction. The reconstructed image isapplied as an input to a computer 36 which stores the image in a massstorage device 38.

Computer 36 also receives commands and scanning parameters from anoperator via console 40 that has a keyboard. An associated display 42,such as a liquid crystal display (LCD) and a cathode ray tube, allowsthe operator to observe the reconstructed image and other data fromcomputer 36. The operator supplied commands and parameters are used bycomputer 36 to provide control signals and information to DAS 32, x-raycontroller 28 and gantry motor controller 30. In addition, computer 36operates a table motor controller 44 which controls a motorized table 46to position patient 22 in gantry 12. Particularly, table 46 movesportions of patient 22 through gantry opening 48. Computer 36, console40, and display 42 are used in the following method, in conjunction witha pointing device and a keyboard. The pointing device is, for example, acontrol on console 40 or a separate device such as a mouse (not shown).

In one embodiment, computer 36 includes a device 50 for reading andwriting onto removable media 52. For example, device 50 is a floppy diskdrive, a CD-R/W drive, or a DVD drive. Correspondingly, media 52 is afloppy disk, a compact disk, or a DVD. Device 50 and media 52 are usedin one embodiment to transfer acquired projection data from imagingsystem 10 to another computer for further processing, or in anotherembodiment to input machine readable instructions that are processed bycomputer 36.

FIG. 3 is a flowchart of an exemplary embodiment of a method 60 foranalyzing a tubular structure in a patient 22 (shown in FIG. 1). Method60 describes a method to guide at least one cursor along a centerline ofa tubular structure, such as a colon, in at least one examination. Thecursor is a visual marker which indicates a three-dimensional location,and may be deposited by a user at a selected location within the tubularstructure, such as three-dimensional views and reformatted slices.Method 60 facilitates computing a local path around the cursor positionwherein the path is the centerline of the tubular structure. Thelocation of the cursor is displayed in three-dimensional views. Axial,Sagittal, Coronal and Oblique slices that contain the cursor can then bedisplayed. Further, if the view is rotated, the angle from the tangentto a centerline of the structure at the current cursor position isstored so that further internal three-dimensional views are displayed atthe same angle from the new tangents, thereby maintaining the sameorientation relative to the structure.

Method 60 includes receiving 62 a cursor first position within adisplayed tubular structure representative of a tubular structure in thepatient, determining 64 a path inside the tubular structure, and moving66 a cursor along the path by a pre-determined distance in apre-determined direction to a cursor second position. Method 60 alsoincludes displaying at least one of a three-dimensional view depictingthe cursor second position, an axial, a sagittal, a coronal, and atleast one oblique slice depicting the cursor second position, whereinthe oblique slice is perpendicular to the tubular structure at thecursor second position. Method 60 also includes displaying an internalthree-dimensional view from the cursor second position, wherein theinternal view is an “endoscopic like” view.

Receiving 62 a cursor first position includes inputting a first cursorposition, determining if the first cursor position is within the tubularstructure, and initializing a computer program installed on computer 36.

In use, an operator inputs into computer 36 a cursor first positioninside the tubular structure and a direction along the tubular structurein which the operator wishes to examine. In one embodiment, the cursorfirst position is input by the operator using the pointing device andthe direction is input by the operator by depressing at least one key onthe keyboard, such as, but not limited to, the forward arrow key and thebackward arrow key. In another embodiment, the cursor first position andthe direction are input by the operator using other conventional datainput methods. Computer 36 receives the operator input and generates athree-dimensional vector including a current cursor position value(CtxCurPos), and a vector direction component (CtxMoveDir). The cursorfirst position is assigned as the CtxCurPos, i.e. a current cursorposition that is within a three-dimensional tubular structure asdepicted on display 42, for example, a colon (not shown). The computerassigns the user selected direction input as the CtxMoveDir, i.e.,computer 36 generates a three-dimensional vector with an origin at theCtxCurPos in the direction of the CtxMoveDir. Additionally, computer 36assigns a gray-level value (Val) to the CtxCurPos. Computer 36 generatesthe vector based only on the received cursor position, i.e., computer 36does not compute the vector (i.e., the path) using both a receivedstarting point and a received ending point. Rather computer 36determines an ending point according to the vector.

Computer 36 then determines whether the cursor is in the tubularstructure. If the gray-level value assigned to the CtxCurPos is betweena minimum voxel value (CtxMinVoxelValue) defining the tubular structureand a maximum voxel value (CtxMaxVoxelValue) defining the tubularstructure, i.e. CtxMinVoxelValue>CtxCurPos<CtxMaxVoxelValue, computer 36then proceeds to initialize the program installed on computer 36.Alternatively, when the CtxCurPos is not between CtxMinVoxelValue andCtxMaxVoxelValue, computer 36 generates a false output and requests theoperator to re-input the CtxCurPos and the CtxMoveDir. Computer 36 thendetermines whether a program installed on computer 36 has beeninitialized. If the program has been initialized, computer 36 continuesmethod 60, if the program has not been initialized, computer 36initializes the program and continues method 60.

FIG. 4 is a flowchart illustrating a portion of method 60 includinginitializing 70 computer 36. Initializing 70 computer 36 includesselecting a plurality of candidate voxels inside the tubular structureand connecting a plurality of the candidate voxels.

In use, selecting a plurality of candidate voxels inside the tubularstructure includes applying a threshold value to the candidate voxels inthe initial gray-level volume, i.e. defining the tubular structure andkeeping nothing but the tubular structure and eliminating all points notlocated in the tubular structure. Initializing 70 is effective if voxelsnot selected are not used in any of the calculation processes describedhereinafter. Alternatively, initialization 70 is implementationdependant and may be bypassed by the operator. In one embodiment, theoperator may view a border of the tubular structure by applying athree-dimensional dilation of two pixels.

FIG. 5 is a flowchart illustrating a portion of method 60 includingdetermining 64 a path inside the tubular structure which includesdetermining 72 a new trajectory and getting 74 a NextPoint point in thetrajectory. Determining 72 a trajectory includes initializing a context,starting a new trajectory using the current CtxCurPos, and setting aninitial search direction.

Computer 36 first determines whether a trajectory context (CtxTraj) isempty or the CtxCurPos has been manually moved. The CtxTraj is a doubledchained list of points with directional information. If the CtxTraj isnot empty and the CtxCurPos has not been manually moved, computer 36continues method 60 and proceeds to getting 74 a next point (NextPoint).If the CtxTraj is empty or the CtxCurPos has been manually moved,computer 36 determines a new path inside the tubular structure.

In use, computer 36 empties a trajectory points list and adds thecurrent CtxCurPos to the trajectory, i.e. sets CtxCurPoint=CtxCurPos.Computer 36 unlocks the trajectory ends to enable computer 36 to addadditional points. Locking a trajectory end prohibits computer 36 frominputting additional trajectory points. Computer 36 then sets a rotationmatrix (CtxRelativeRotMat)= a three-dimensional identity matrix. TheCtxRelativeRotMat is used by computer 36 to obtain the initial searchdirection using the CtxCurPos in the direction of the CtxMoveDir asdescribed herein. In one embodiment, x and y rotations, i.e. thetwo-dimensional screen coordinates, are used to generate athree-dimensional rotation matrix. Computer 36 then determines whether apredefined tubular structure topology is available. Computer 36determines an initial search direction, i.e. forward (FwDir) or backward(BkDir) according to FIG. 5.

FIG. 6 is a flowchart illustrating a portion of method 60 includinggetting 74 a NextPoint point. Getting 74 a NextPoint point includesdetermining if the trajectory end is locked. In one embodiment, if thetrajectory end is locked, computer 36 determines if the trajectory endis less than three points forward in the CtxMoveDir, and if thetrajectory end is less than three points forward in the move direction,computer 36 sets a next point (NextPoint) equal to null and continues.If the trajectory end is locked and the trajectory point is not lessthan three points forward in the CtxMoveDir, computer 36 sets NextPointequal to a trajectory point subsequent to the CtxCurPoint in theCtxMoveDir and continues the program. Alternatively, if the trajectoryend is not locked, computer 36 sets NextPoint equal to a trajectorypoint subsequent to the CtxCurPoint in the CtxMoveDir. Recomputing thetrajectory when the aimed trajectory is less than three points from thetrajectory end facilitates ensuring that the trajectory remains close tothe center of the tubular structure.

Referring again to FIG. 3, computer 36 then verifies that the CtxTraj isnot locked and NextPoint equals null. If yes, i.e. the CtxTraj is notlocked and NextPoint equals null, computer 36 computes new points usinga global approach as explained in greater detail below. Alternatively,computer 36 queries NextPoint to verify if NextPoint equals null. If no,i.e., next point does not equal null, computer 36 proceeds with method60. If yes, NextPoint is null, forward progression stops and theoperator can move backwards or restart from another point.Alternatively, the trajectory is recomputed if it remains less than 3points until the end. Recomputing the trajectory facilitates ensuringthat the trajectory remains close to the center of the tubularstructure. Additionally, through locking the trajectory (CtxTraj) and/orchecking NextPoint for being null, computer 36 is able to determine whento stop progression either forward or backward.

FIG. 7 is a flowchart illustrating a portion of method 60 includingcomputing 80 new points using a global approach. Computing 80 new pointsusing a global approach includes setting 82 a sphere of interest,computing 84 a distance to CtxCurPoint, computing 86 a distance to atubular structure border, getting 88 a furthest centered point(FinalPoint), and computing 90 a best path from the CtxCurPoint to theFinalPoint (i.e., endpoint).

FIG. 8 is a pictorial view of a portion of method 60 including setting82 a sphere of interest. Setting 82 a sphere of interest includesselecting a sub-volume containing the CtxCurPoint and a plurality ofpoints in the CtxMoveDir, wherein a directional vector in the CtxMoveDiris defined for the CtxCurPoint.

In use, and referring to FIGS. 7 and 8, the operator selects asub-volume which includes the CtxCurPoint, i.e., a three-dimensionalpoint, and the DirToGo, i.e., a three-dimensional vector. In oneembodiment, a radius of the sphere (CtxSphereRadius) is fixed. If theDirToGo vector is normalized then CenterofSphere is determined accordingto:${{Center}\quad {Of}\quad {Sphere}} = {{CtxCurPoint} + {4 \times \left( \frac{{Ctx}\quad {Sphere}\quad {Radius}}{5} \right) \times {Dir}\quad {To}\quad {Go}}}$

Referring again to FIG. 7, the volume is then re-initialized inaccordance with FIG. 5 described previously herein and computer 36instructs the program to compute 84 a distance to CtxCurPoint asdescribed herein.

FIG. 9 is a flowchart of a portion of method 60 including computing 84 adistance to a CtxCurPoint. In use, computing 84 a distance to a currentpoint on the trajectory (CtxCurPoint) includes, for all points (P),generating a distance map (DistMap(P))=65535. If a goal point is giventhen the initial value (Initvalue)=65535. If the goal point is notgiven, then Initvalue=0. Then computer 36 then initiates at least one ofa propagate forward and a propagate backward program.

FIG. 10 is a flowchart of a portion of method 60 including propagating92 forward and propagating 94 backward. If a propagation way is forwardor the propagation way is backward, computer 36 performs the method asillustrated in FIG. 10. Computer 36 then computes a distance to theborder of the tubular structure.

FIG. 11 is a flowchart of a portion of method 60 including computing 86a distance to a border of a tubular structure. In one embodiment,computer 36 uses the same method, i.e. as illustrated in FIG. 11 tocompute the distance to a border of a tubular structure as is used tocompute the distance to the CtxCurPoint. Computer 36 then proceeds togetting 88 the furthest point.

Referring again to FIG. 7, computing 80 new points using a globalapproach also includes getting 88 the furthest point (FinalPoint). FIG.11 is a flowchart of a portion of method 60 getting 88 the furthestpoint in accordance with:

Dmin=min distance to CtxCurPoint

Dmax=max distance to CtxCurPoint

${Dfar} = \frac{\left( {4 \times D\quad \max} \right) + \left( {1 \times D\quad \min} \right)}{5}$

where the distances to CtxCurPoint (D 0) and distances to the border ofthe tubular structure are determined using the distance maps describepreviously herein.

Getting a furthest centered point (FinalPoint) also includes settingCandidates= points P such that D(CtxCurPoint,P)>Dfar. The FinalPoint isthen computed according to: FinalPoint=point included in Candidates withthe maximum distance to the border of the tubular structure.

FIG. 12 is a flowchart of a portion of method 60 including computing 90(shown in FIG. 7) a best path from the CtxCurPoint to the FinalPointwhich includes propagating 100 a distance forward and propagating 102 adistance backward as illustrated in FIG. 13. Propagating 100 forward andpropagating 102 backward includes propagating 104 from a first line andpropagating 106 from a second line, i.e. distance propagation betweenlines, and propagating 108 along an x axis, i.e. distance propagationinside a line. Propagating 104 from a first line and propagating 106from a second line is illustrated in FIG. 14. Propagating 108 along anx-axis is illustrated in FIG. 15.

As shown in FIGS. 12-15, the cos(t) function is constructed accordingto:

Cost(P _(n+1))=Minimum(Cost(P _(n+1)), Cost(P _(n))+V(P _(n+1)))

where n is a step along the construction path, P_(n) denotes a point atstep n, V(P_(n)) is a distance to the border of the tube from thecorresponding point, and paths are along the six faces of a given voxel.For non-isotropic voxels, the six faces of the voxel form aparallelepiped. For isotropic voxels, the six faces of the voxel form acube.

Using this function, a sequential process is applied to compute thefinal result. Beginning from point 0, i.e. starting point, at cos(t) 0.All others points have infinite cos(t). The values are then propagatedinside lines, to the left or right points, and then forward acrosslines, to lines at y+1 or z+1 from y,z. The process is then repeated inthe other direction to lines at y−1 and z−1 from y,z. The process willstop after a given maximum number of iterations once the target pointhas been reached by a propagated “wave”. A direction code to a bestpredecessor point is stored along with the value.

To improve performance, an array of active lines is also used. The arraycontains a 2 bit word for every line, which is decremented from 2 justafter new values have been assigned in a given line, and then to 0,after the line has been processed twice, forward and backward, withoutany change in the values. This array is used to skip lines that have notyet been reached by the propagation process or for which it hasconverged.

This process may be aborted by the operator using a feedback function. Ascaling feature is also provided to prevent overflows (cos(t)s arestored on 13 bit values for very long paths on noisy objects.) Overflowswill result in a failure to detect that targets have been reached. Thiswill be reported and may not cause wrong identifications. The best pathis computed by unfolding the direction codes from the target point tothe initial seed.

Referring again to FIG. 3, once computer 36 has completed computing 80new points using a global approach, computer 36 checks for half turns inthe tubular structure. FIG. 16 illustrates a portion of method 60including checking 110 for half turns in the tubular structure. FIG. 17is an illustrative example of checking 100 for half turns in the tubularstructure. Checking 110 for half turns checks the trajectory toascertain whether the trajectory contains half-turns or loops asillustrated in FIG. 17 and cuts the trajectory if either the half-turnor loop is detected.

After computer 36 has completed checking 110 for half turns computer 36returns to getting 74 a NextPoint point in the trajectory as describedpreviously herein. If the NextPoint is not null, computer 36 movestoward the NextPoint as described later herein. If the NextPoint isnull, computer 36 computes new points using a local approach.

FIG. 18 is a flowchart illustrating computing 120 new points using alocal approach. Computing 120 new points using a local approach includesdeleting trajectory points subsequent to CtxCurPoint in the CtxMoveDir,computing 122 vector data for PrevPoint and CtxMoveDir, and computing124 vector data for Point and CtxMoveDir.

FIGS. 19 and 20 are pictorial views illustrating a method of computing120 new points using a local approach. The local approach is based onassumptions on the topology of the tube such as there is no junction,i.e. there is only one branch, variations of the diameter of the tubeare smooth “enough”, and turns are smooth. Therefore, using the localapproach, at a given point, vectors are thrown (ray casting) in theforward half-plane. The vector's end at the border of the tube and thevector lengths are stored in computer 36. In one embodiment, theresulting directional vector is the sum of thrown vectors ponderated bytheir length such that the further a border is in a direction, the morethat direction contributes in the resulting vector, which is the normalcase. If a reduction in the average length of the thrown vectors isdetected, then there is a diameter reduction straight forward. Moreweight is then given to long vectors and shrink the “angle of vision” toavoid half-turns and the resulting vector is the sum of a selection ofthrown vectors (those included in the angle of vision) ponderated by apower of their length (so that the faster the reduction is, the higheris the.power). It is a way to force the resulting vector to tend to thelongest thrown vector in the tube.

Referring again to FIG. 3, after computing 120 new points using a localapproach, computer 36 initiates checking 110 for half turns as describedpreviously herein. Computer 36 then initiates getting 74 next point asdescribed previously herein. Computer 36 then checks to see ifNextPoint=null. If NextPoint is equal to null, then computer 36 ends theprogram. If the NextPoint is not equal to null, computer 36 initiatesmoving 66 towards NextPoint.

FIG. 21 is a portion of method 60 including moving 66 towards the nextpoint (NextPoint). Given the current and next points in the trajectorycontext, and given the current cursor position, computer 36 computes anew cursor position in accordance with FIG. 21.

FIG. 22 is a portion of method 60 which includes computing 130 adirection to look. Once the trajectory context and the current cursorposition have been determined, computing 130 a direction to lookproceeds in accordance with FIG. 22. In use, if the operator moves thecursor, a new trajectory is begun and the relative rotation matrix isreinitialized. Further, each time the operator changes the orientationof an endoscopic view, the relative rotation matrix is computed, suchthat the view retains the same angle relative to the tracked trajectory

In one embodiment, method 60 facilitates guiding an operator along thetubular structure during an examination. Further, since method 60 relieson local computations, it facilitates a reduction in setup time. Method60 also avoids the definition of start and endpoints and thus reducesthe time required by an operator to perform an examination.Additionally, in the case of multiple acquisitions of the samestructure, the same starting point is identified accurately for all datasets, then because all cursors travel the same distances along thecenterline of the structure, the cursors will identify the same locationinside this structure. The only user input required in this case is thedefinition of the starting point for all examinations.

In another embodiment, a method 200 for reviewing a tubular structureover a passage of time includes providing 202 at least a firstthree-dimensional data set at a first time and a secondthree-dimensional data set at a second time representative of the sametubular structure. Method 200 facilitates assisting operators during apatient examination by allowing the operator to compare the results of aprevious examination with the results of a current examination, at thesame time on computer 36, and to formulate treatment based on thedifferences in these results. Method 200 also includes generating 204 afirst view of the first three-dimensional data set and a second view ofthe second three-dimensional data set, and positioning 206 a firstcursor at a first three-dimensional location in the within the firstview and positioning a second cursor at a first three-dimensionallocation within the second view. Method 200 also includes determining208 a path inside the first tubular structure and the second tubularstructure, defining 210 a direction from the cursor position in at leastone of the first view and the second view, and moving 212 the firstcursor along the determined path by a pre-determined distance in apre-determined direction to first cursor second position and moving thesecond cursor along the determined path by a pre-determined distance ina pre-determined direction to second cursor second position.

Method 200 also includes displaying 220 at least one of athree-dimensional view depicting the first cursor second position, anaxial view depicting the first cursor second position, a sagittal viewdepicting the first cursor second position, a coronal view depicting thefirst cursor second position, and at least one oblique slice depictingthe first cursor second position, and displaying 222 an internalthree-dimensional view from at least one of the first cursor secondposition and the second cursor second position. Method 200 fartherincludes receiving 224 a directional input and moving at least one ofthe first cursor and the second cursor the pre-determined distance alongthe pre-determined path according to the received directional input anddisplaying 226 at least one internal three-dimensional view of thetubular structure from at least one of the first cursor second positionand the second cursor second position directed along the axis of thetubular structure at the respective cursor second position.

Embodiments of the present invention are applicable to selection andanalysis of many types of tubular structures, including vascularstructures, coronary vessels, and airways. In addition, althoughembodiments of the present invention have been described in conjunctionwith a CT imaging systems 10, it will be understood that the presentinvention is also applicable to other types of imaging systems andimages obtained from such systems, as well. Examples of such other typesof imaging systems used in other embodiments of the present inventioninclude MR imaging systems and 3-D x-ray imaging systems. In addition,some embodiments of the present invention utilize data computers anddisplays that are not themselves part of any imaging system. In thesecases, the computers obtain data from one or more separate imagingsystems, such as via tape, disk, or other storage media, or via anetwork. At least one such embodiment is configured to accept, handle,and process data from more than one type of imaging system.

Although the methods described herein are in the context of a computedtomography system, the methods are not limited to practice with computedtomography systems and can be utilized in many different imagingmodalities. For example, the methods can be used in connection withx-ray, magnetic resonance, positron emission tomography, ultrasound, andother imaging modalities.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

What is claimed is:
 1. A method for analyzing a tubular structure in apatient, said method comprising: receiving a cursor first positionwithin a displayed tubular structure representative of the tubularstructure in the patient; determining a path inside the tubularstructure based only on the received cursor first position; and moving acursor along the path by a pre-determined distance in a pre-determineddirection to a cursor second position.
 2. A method in accordance withclaim 1 further comprising generating at least one image of the tubularstructure using a three-dimensional data set.
 3. A method in accordancewith claim 1 further comprising displaying at least one of athree-dimensional view depicting the cursor second position, an axialview depicting the cursor second position, a sagittal view depicting thecursor second position, a coronal view depicting the cursor secondposition, and at least one oblique slice depicting the cursor secondposition.
 4. A method in accordance with claim 1 further comprisingdisplaying an internal three-dimensional view from the cursor secondposition.
 5. A method in accordance with claim 1 wherein moving a cursoralong the path by a pre-determined distance in a pre-determineddirection to the cursor second position further comprises: receiving adirectional input; and moving the cursor the pre-determined distancealong the pre-determined path according to the received directionalinput.
 6. A method in accordance with claim 1 further comprisingdisplaying at least one oblique slice comprising the cursor secondposition and forming an angle perpendicular to the tubular structure atthe cursor second position.
 7. A method in accordance with claim 1further comprising displaying at least one internal three-dimensionalview of the tubular structure from the cursor second position directedalong the axis of the tubular structure at the cursor second position.8. A method in accordance with claim 1 further comprising displaying atleast one internal three-dimensional view of the tubular structure atthe cursor second position such that the view forms an angle with theaxis of the tubular structure at the cursor second position.
 9. A methodin accordance with claim 1 further comprising displaying at least oneoblique slice of the tubular structure at the cursor second positionsuch that the oblique slice forms an angle perpendicular with thetubular structure at the cursor second position.
 10. A method inaccordance with claim 1 further comprising determining when to stopprogression of the cursor.
 11. A method in accordance with claim 8further comprising displaying at least one internal three-dimensionalview of the tubular structure at the cursor second position such thatthe view forms an angle with the axis of the tubular structure at thecursor second position that is substantially the same as an angle fromthe cursor first position such that an orientation of the view at thecursor second position.
 12. A method for reviewing a tubular structureover a passage of time, said method comprising: providing at least afirst three-dimensional data set at a first time and a secondthree-dimensional data set at a second time representative of the sametubular structure; generating a first view of the firstthree-dimensional data set and a second view of the secondthree-dimensional data set; positioning a first cursor at a firstthree-dimensional location within the first view and positioning asecond cursor at a first three-dimensional location within the secondview corresponding to the first cursor location in the first view;determining a path inside the tubular structure; defining a directionfrom the cursor position in at least one of the first view and thesecond view; and moving the first cursor along the determined path by apre-determined distance in a pre-determined direction to first cursorsecond position and moving the second cursor along the determined pathby a pre-determined distance in a pre-determined direction to secondcursor second position.
 13. A method in accordance with claim 12 furthercomprising displaying at least one of a three-dimensional view depictingthe first cursor second position, an axial view depicting the firstcursor second position, a sagittal view depicting the first cursorsecond position, a coronal view depicting the first cursor secondposition, and at least one oblique slice depicting the first cursorsecond position.
 14. A method in accordance with claim 12 furthercomprising displaying an internal three-dimensional view from at leastone of the first cursor second position and the second cursor secondposition.
 15. A method in accordance with claim 12 wherein moving thefirst cursor along the determined path by a pre-determined distance in apre-determined direction to first cursor second position and moving thesecond cursor along the determined path by a pre-determined distance ina pre-determined direction to second cursor second position furthercomprises: receiving a directional input; and moving at least one of thefirst cursor and the second cursor the pre-determined distance along thepre-determined path according to the received directional input.
 16. Amethod in accordance with claim 12 further comprising displaying atleast one internal three-dimensional view of the tubular structure fromat least one of the first cursor second position and the second cursorsecond position directed along the axis of the tubular structure at therespective cursor second position.
 17. A computer readable mediumencoded with a program executable by a computer for analyzing a tubularstructure in a patient, said program configured to instruct the computerto: receive a cursor first position within a displayed tubular structurerepresentative of a tubular structure in a patient; determine a pathinside the tubular structure based only on the received cursor firstposition, wherein the determined path includes a determined endpoint;and move a cursor along the path by a pre-determined distance in apre-determined direction to a cursor second position.
 18. A computerreadable medium in accordance with claim 17 wherein said computerfurther configured to generate at least one image of the tubularstructure using a three-dimensional data set.
 19. A computer readablemedium in accordance with claim 17 wherein said computer furtherconfigured to display at least one of a three-dimensional view depictingthe cursor second position, an axial view depicting the cursor secondposition, a sagittal view depicting the cursor second position, acoronal view depicting the cursor second position, and at least oneoblique slice depicting the cursor second position.
 20. A computerreadable medium in accordance with claim 17 wherein said computerfurther configured to display an internal three-dimensional view fromthe cursor second position.
 21. A computer readable medium in accordancewith claim 17 wherein to move a cursor along the path by apre-determined distance in a pre-determined direction to a cursor secondposition said computer further configured to: receive a directionalinput; and move the cursor the pre-determined distance along thepre-determined path according to the received directional input.
 22. Acomputer readable medium in accordance with claim 17 wherein saidcomputer further configured to display at least one oblique slicecomprising the cursor second position and forming an angle perpendicularto the tubular structure at the cursor second position.
 23. A computerreadable medium in accordance with claim 17 wherein said computerfurther configured to display at least one internal three-dimensionalview of the tubular structure from the cursor second position directedalong the axis of the tubular structure at the cursor second position.24. A medical imaging system for analyzing a tubular structure in apatient, said medical imaging system comprising: a detector array; atleast one radiation source; and a computer coupled to said detectorarray and radiation source and configured to: receive a cursor firstposition within a displayed tubular structure representative of thetubular structure in the patient; determine a path including an endpointinside the tubular structure based only on the received cursor firstposition; and move a cursor along the path by a pre-determined distancein a pre-determined direction to a cursor second position.
 25. A medicalimaging system in accordance with claim 24 wherein to analyze a tubularstructure in a patient, said computer further configured to generate atleast one image of the tubular structure using a three-dimensional dataset.
 26. A medical imaging system in accordance with claim 24 wherein toanalyze a tubular structure in a patient, said computer furtherconfigured to display at least one of a three-dimensional view depictingthe cursor second position, an axial view depicting the cursor secondposition, a sagittal view depicting the cursor second position, acoronal view depicting the cursor second position, and at least oneoblique slice depicting the cursor second position.
 27. A medicalimaging system in accordance with claim 24 wherein to analyze a tubularstructure in a patient, said computer further configured to display aninternal three-dimensional view from the cursor second position.
 28. Amedical imaging system in accordance with claim 24 as wherein to move acursor along the path by a pre-determined distance in a pre-determineddirection to a second position, said computer further configured to:receive a directional input; and move the cursor the pre-determineddistance along the pre-determined path according to the receiveddirectional input.
 29. A medical imaging system in accordance with claim24 wherein to analyze a tubular structure in a patient, said computerfurther configured to display at least one oblique slice comprising thecursor second position and forming an angle perpendicular to the tubularstructure at the cursor second position.
 30. A medical imaging system inaccordance with claim 24 wherein to analyze a tubular structure in apatient, said computer further configured to display at least oneinternal three-dimensional view of the tubular structure from the cursorsecond position directed along the axis of the tubular structure at thecursor second position.
 31. A medical imaging system in accordance withclaim 24 wherein said computer further configured to move a cursor alongthe path by a pre-determined distance in a pre-determined direction to acursor second position wherein the cursor second position is thedetermined endpoint.